The present invention relates generally to a laminar thermoplastic resin structure capable of retaining high bonding strength at elevated temperatures and more particularly to a laminar thermoplastic resin structure comprising a plurality of layers bonded with a layer or layers of a maleic acid-modified block copolymer interposed therebetween.
High bonding strength retentivity at elevated temperatures is desirable, for example, when a laminar structure is used as a food packaging material which is subjected to retort sterilization, particularly high temperature retort sterilization carried out at 130.degree. C. or higher, or is required at joints of hot water pipes.
Most of the adhesives heretofore known to have satisfactory bonding strength at elevated temperatures are of thermosetting type such as polyurethane resin adhesives and epoxy resin adhesives. These adhesives leave much to be desired with respect to handling conditions.
As adhesives of thermoplastic type, on the other hand, those having noticeably reduced bonding strength at 100.degree. C. or higher, such as styrene-butadiene block copolymers and ethylene-vinyl acetate copolymers, or those having excellent adhesiveness at high temperatures with respect limitedly to specific resins, for example, polycarbonates to polyesters have been used. However, thermoplastic adhesives possessing improved adhesiveness with respect to a wide variety of thermoplastic resins at high temperatures have not yet been developed as far as we are aware.